Process and apparatus for cracking oil



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IROCESS AND APPARATUS FOR CRACKING OIL I Filed March 26, 1929 CONDENSERCOMPress 0 frieze/7hr Patented May 5, 1936 UNITED STATES PATENT OFFICEPROCESS AND APPARATUS FOR CRACKING OIL charging stock is maintained inthe liquid phase.

during heating to cracking temperatures, by high pressures, the carbonformed as the liquid oil is decomposed being of a gummy nature andtending to deposit on the heating surfaces of the apparatus and causinghot spots thereon as is commonly understood. In processes for crackingin the vapor phase, the carbon precipitant is more in the nature of afinely divided powder which may, to a certain extent, be carried fromthe heating zone by passing the vapors through at a high velocity, butprior to the heating of the oil in the vapor phase, considerabledeposits of carbon are frequently formed in the initial heating andvaporization of the charging stock, as a certain amount of cracking maytake place in this operation. In all processes of this nature heretoforeemployed, insofar as I am aware, heat supplied to the charging stock,either merely to vaporize the stock or to effect its thermaldecomposition, is transmitted from the heat source through the walls ofthe heating elements.

In accordance with the present invention, hydrocarbon oils may besubjected to cracking and the system be kept comparatively free fromdeposited carbon, this being accomplished mainly due to the fact thatinstead of heating and vaporizing. the stock by heat transmitted from anexternal heat supply through the wallsof the heating elements of theequipment, the liquid charge is heated and vaporized by admixture withpreviously vaporized and superheated stock. The present method ofdistillation includes generally, the vaporization of an entire orpredetermined portion of a feed liquid charge by mixing the charge witha portion of the superheated vapors from previously vaporized stock, theheat of superheat in these vapors being sufficient to vaporize and, if.it is desired, to partially crack the charging stock. The vaporousmixture from this operation is then superheated and a portion of thesuperheated vapors utilized in heating and vaporizing subsequent heatedliquid. As viewed in another aspect, the heating of the charging stockmay be considered as being effected by recycling through the system apredetermined portion of superheated vapor product, the heat of 5superheat in said portion being suflicient to prodtuce the desiredheating and vaporization of the s cc As a result of the initial heatingand vaporization of the charging stock by admixture with 10, previouslysuperheated vapors, whatever carbon is formed during this operation isprecipitated in the vapor body as a powder and may be convenientlyremoved as will hereinafter be described. Carbon formed in thesubsequent steps 15 of superheating the vapor mixture is also throwninto the vapor stream as a dry powder and may be easily settled out ofthe final superheated vapors.

The apparatus utilized in carrying out the method outlined lends itselfparticularly to the maintaining of high efliciency in operation and alsoin facilitating control of the system. One particular feature ofadvantage resides in the compressing of that portion of the superheatedvapors to be used in heating the charge, and subsequently dischargingthe compressed vapors at high velocity along with the feed drawn byinjector action into the vapor stream, into a reaction chamber whereinthe feed is subjected to vaporization and wherein carbonaceous bodiesand any unvaporized charge settle out. The arrangement of the systemalso permits accurate control of the recycled superheated vapors bymerely controlling the pressure in the system, or as will later bepointed out, the amount of recycled superheated vapors may bepredetermined by controlling, in effect, the density of the superheatedvapors before their intake to the compressor.

The above and additional features and advantages of the invention willbe best and most fully discussed in the following detailed descriptionof the system, reference being had throughout the description to theaccompanying drawing, in which the apparatus employed in carrying out mycracking process is illustrated diagrammatically.

The charging stock, which may be crude petroleum or any suitablefraction thereof such as fuel oil, is supplied to the feed pump [0 froma suitable source, for instance, feed line H, after having previouslypassed through the heat changer l2, in which the oil is brought intoheat transferring relation with. cracked vap rs. passin t the refluxtower, as will hereinafter appear. The feed is discharged by the pumpthrough line l3 into the supply tank I 4, the liquid in the latterpreferably being maintained at a substantially constant level by meansof the float controlled valve [5 which controls the flow of steam to thepump through line l6. The feed liquid line I8 extends from the interiorof tank l4 beneath the liquid level therein, and opens into thedischarge throat I9 ofthe compressor 26. drawn from the supply tankthrough line l8 into the compressor discharge I!) by the action ofvapors being discharged from the compressor at a high velocity as willlater be described.

It may be noted at this point that the vapors discharged from the.compressor are superheated considerably above their saturationtemperatures, the heat of superheat of the vapors being sufficient tovaporize all or a predetermined portion of the charging stock mixed withthe vapors. The liquid and vapor mixture from throat l9 passes into themixing chamber 2| wherein the liquid and vapor are thoroughly mixed andin which partial vaporization of the feed liquid may take place. Themixture within passage 2| is discharged into the reaction chamber 22,the latter preferably being of increased volume in order that the fluidstream may be slowed down and any carbonaceous bodies resulting from theheating of the feed, and alsoa'ny unvaporized portions of the feed, maysettle out in the bottom of the chamber. In the reaction chamber theheating and vaporization of the feed is carried to completion, and uponcomplete vaporization of the chargea certain amount of cracking may takeplace, this however being dependent upon the nature'of the stock andalso the available superheat in the vapors discharged from thecompressor. In certain instances it may not be desirable to vaporize allof the feed liquid taken into the chamber through line IS, in whichevent the amount of superheat inthe vapormay be predetermined as willlater be described, to vaporize only the desired portion of the feed.The reaction chamber 22 may be of any suitable design, preferablyhowever of such nature as to assure the removal of carbon particles fromthe vapors discharged from the chamber. V

The vapors in line 23 leading from the reaction chamber are passedthrough the pipe coil 24 in the superheater 25, the superheater servingto complete the cracking of the vapors and to heat the vapors to providesuilicient available superheat for vaporizing subsequent feed liquid.The heated vapors from the superheater are conducted through line 26into the carbon trap 21 wheree in the powdery carbon particlesformedduring the passage of the vapors through the superheater are settled outin the bottom of thetrap. The residual carbonaceous materials in thebottoms of the reaction chamber and carbon'trap are removed by means ofsuitable ejectors 29 and 30, respectively. Outlet lines 3| and 32 leadinto the ejectors and materials settling in the bottoms of the reactionchamber and carbon trap are drawn through the outlet lines into theejectors and subsequently discharged along with the ejector operatingfluid.

A portion of the superheated vapors in chamber 2l is delivered throughline 34 to the com: pressor 20, the latter being driven by motor 35 andbeing positioned at any suitable height above the feed liquid in thesupply tank. The vapors are compressed in compressor 20 to such anextent as to enable their being discharged through the The feed isoutlet throat l9 at a high velocity and at a rate such as to draw thefeed liquid from line l8 into the vapor stream as heretofore mentioned.It may be noted that the vapors also are further superheated somewhat byvirtue of their being compressed. In addition to the injector action fordrawing the feed through line It! into the mixing chamber, there is acertain amount of pressure applied to the surface of the liquid insupply tank M. The pressure of the superheated vapors discharged fromthe heater 25 is communicated to space Na in the supply tank by line 3!leading into the discharge vapor line 36, the application of pressure tothe liquid surface in. the supply tank serving not only to assist in thedelivery of feed through line l8 but also to maintain an even pressurein the tank regardless of possible irregular operation of the supplypump Ill. The invention contemplates, in a broad sense, the use of any 7suitable means for effecting recirculation of a portion of thesuperheated vapors in the system and for mixing the recycled vapor withfeed liquid, the use of a compressor and in the manner described, aswell as the introduction of feed liquid by injector action into thevapor stream after compression, however, being preferred.

That portion of the superheated vapors not recycled to the compressorline 34, passes through the outline line 36 through apparatus, generallyindicated at 38, for separating the cracked vapors into the desiredconstituents. Any suitable equipment may be used in subjecting thevapors to fractionation, or separation, the illustrated apparatus beingtypical only. The vapors in line 36 are first conducted through the heatexchanger l2, wherein the superheat in the vapors may be transferred tothe feed liquid in line II, the vapors then flowing through line 38ainto the reflux tower 39. The heavier and undesirable fractions in theproduct vapors are separated 'within the reflux tower, and are drawnfrom the base of the tower through line 39a, the separated vaporsflowing from the top of the column through line 40 into the condenser4|. The fractions condensed in condenser 4| being separated from theuncondensible or fixed gases in the gas trap 42 are discharged from thesystem through line 43. "The pressure conditions in the systempreferably are regulated by means of the back pressure valve 44 in thedischarge line 43.

By adjusting the back pressure'valve 44 to control the pressure of thevapor in the system beyond the superheater, the amount of vaporsrecycled through the compressor, and therefore the amount of heatcontained in these vapors, is likewise controlled. For instance, byadjusting valve 44 to build up the pressure in the system, the resultingeffect on the vapors is to increase their density and therefore the heatcontent of a given volume-of the vapors. Assuming the compressor tooperate at constant volumetric displacement, although this may notnecessarily be the case, the effect had by increasing the pressure ofthe vapors and therefore their density, is to increase accordingly theheat contents of the vapors admixed with the feed liquid. The amount ofrecycled vapors and therefore the degree of heating of the feed liquidthus being controllable by the back pressure valve 44, the latter may beadjusted to effect any predetermined degree of heating of the feed.Substantially the same effect may be gained by placing the back pressurevalves in the system at any desired location beyond the point of takingoif the vapors to be recycled, for instance by back pressure valves 10-catedin the vapor lines at 45 or 46 beyond the carbon trap, although itis preferred that the control valve be located at 44/ in order tomaintain more even pressure conditions throughout the entire system.

The temperature to which the vapors are heated in the super-heater maybe determined in accordance with the nature of the charging stock andalso the extent to which it is desired to carry the cracking reaction.As a typical temperature range to which the vapors may be superheated, Imay state that using a charging stock of fuel oil, the outlet vaportemperature at the superheater may be in the neighborhood of from 1200F. to 1400 F. It will be understood that instead of superheating thevapors excessively to have available sufficient heat for subsequentlyvaporizing the feed by admixture with a portion of the heated vapors,the available heat may be increased or decreased by correspondinglycontrolling the flow of recycled vapors. And although the quantity ofrecycled vapors might be regulated by controlling the speed of operationof the compressor, a more simplified and accurate control is maintained,as hereinabove described, merely by regulating the pressure of thevapors. The operating pressure in the system therefore may vary withinsuch limits as may be necessary to effect the necessary heat supply tothe feed, a typical pressure range, however, may be given as from 5 to200 pounds per square inch. It will be understood, of course, that theoperating temperatures and pressures in the system are not limited tothe typical values given.

Due to the nature of the successive operations of initially heating andvaporizing the feed", and subsequently subjecting the vapors tosuperheating, it is assured that whatever carbon is formed resultingfrom the heating of the oil is of such nature, and is precipitated undersuch conditions, as to render it readily removable from the system.Carbon initially formed upon vaporization of the feed in the reactionchamber is efiectively removed as heretofore described, and during thesubsequent heating stage within the pipe coils of the superheater apowdery carbon precipitant is formed which is readily entrained in thehigh velocity vapor stream and carried into the carbon trap whereinfinal settling out and separation of the carbonaceous bodies takesplace.

In starting operations the apparatus may be brought up to near thenormal operating temperatures before putting oil into the system, byfiring the superheater and introducing vapors or gases into the systemthrough inlet II to prevent overheating of the superhater tubes as theapparatus is preliminarily heated. Natural gas or steam may for examplebe used for this purpose. Valve 45 may at first be kept nearly closed sothat the gas taken into the supply tank l4 through lines I l and I3 willbe recycled by the compressor through lines l8 and I9 into the reactionchamber and thence through the superheater. During the preliminaryheating period it will only be necessary to maintain a circulation ofgases through the superheater sufficient to prevent overheating untilthe superheater is brought up to temperature. The heated gases will alsoserve to preheat the reaction chamber and carbon trap. After theapparatus has been heated to the desired temperatures, feed liquid willbe introduced to the system through inlet line H, and valve 45 graduallyopened as the feed is subjected to vaporization and the oil vaporsdisplace the previously entered gases. As will be readily understood,the presence of the heated gases within the system will serve to effectthe delivery of feed oil from the supply tank to the compressor outlet,and to initially vaporize the feed, as well as oil vapors.

It will be'understood the drawing and description are to be consideredmerely as illustrative of and not restrictive on the broader claimsappended hereto, for various changes in design, structure andarrangement may be made without departing from the spirit and scope ofsaid claims.

l. The method of distilling petroleum oil that includes injecting feedoil into a chamber with superheated vapors from previously vaporizedfeed oil thereby vaporizing a portion of said feed oil, withdrawing andseparating from the resulting mixture the unvaporized residual liquid,superheating and cracking vapors discharged from said chamber, returninga portion only of the superheatedand cracked vapors to said chambertogether with subsequent feed oil to be vaporized and subjecting theremaining superheated and cracked vapors to condensation.

2'. The method of distilling petroleum oil that includes drawing feedoil into a stream of superheated vapors from previously vaporized feedoil thereby vaporizing a portion of said feed oil and discharging themixture so formed into a chamber, withdrawing and separating from theresulting mixture the unvaporized residual liquid, superheating andcracking vapors discharged from said chamber, returning a portion onlyof the superheated and cracked vapors to said chamber together withsubsequent feed oil to be vaporized and subjecting the remainingsuperheated and cracked vapors to condensation.

3- The method of distilling petroleum oil that includes drawing feed oninto a stream of super heated vapors from previously vaporized feed oilthereby vaporizing a portion of said feed oil and discharging themixture so formed into a chamber, withdrawing and separating from theresulting mixture the unvaporized residual superheating and cracking allof the vapors discharged from said chamber, returning a portion only ofthe superheated and cracked vapors to said chamber together withsubsequent feed oil to be vaporized, and subjecting the remainingsuperheated and cracked vapors to condensation, and regulating thedegree of heating of the feed by controlling the quantity of superheatedvapors returned to the chamber.

4. The method of distilling petroleum oil that includes drawing feed oilinto a stream of superheated vapors from previously vaporized feed oilthereby vaporizing a portion of said feed oil and discharging themixture so formed into a chamber, withdrawing and separating from theresulting mixture the unvaporized residual liquid, superheating andcracking all of the vapors discharged from said chamber, compressing aportion only of the superheated vapors, and subjecting the remainingsuperheated and cracked vapors to condensation, and returning thecompressed vapors to said chamber with feed oil to be vaporized.

5. A petroleum distillation system embodying a reaction chamber, asuperheater communicating with said chamber and adapted to receive andcrack vapors removed from the chamber, means for compressing a portiononly of the superheated vapors removed from said superheater,

means for subjecting the remaining superheated vapors to condensation,means for withdrawing from said chamber the residual unvaporized feed,separately from the vapors, as such residuum'is formed, and means formixing the vapors after compression with feed liquid and for deliveringthe mixture to said reaction chamber.

6. A distillation system embodying a reaction chamber, a heatercommunicating with said chamber and adapted to receive and superheatvapors from the chamber, means for withdrawing residuum from saidchamber separately from the vapors, a vapor passage leading from saidheater, a compressor communicating with said passage and adapted tocompress a portion of the superheated vapors from said heater, a liquidfeed supply chamber communicating with said passage and the pressure inthe passage being applied to the surface of the liquid in said supplychamber, means for delivering feed liquid to the supply chamber, acompressor outlet line communicating with the reaction chamber, thecompressed vapors being discharged at high velocity through the outletline, a feed line extending from beneath the liquid level in said supplychamber and opening into said compressor outlet line, the feed liquidbeing drawn into the last mentioned line by the high velocity vapors.

7. A distillation system embodying a reaction chamber, a heatercommunicating with said chamber and adapted to receive and super-heatvapors from the chamber, means for withdrawing residuum from saidchamber separately from the vapors, a vapor passage leading from saidheater, a compressor communicating with said passage and adapted tocompress a portion of the superheated vapors from said heater,adjustable means for regulating the pressure in said vapor passage, aliquid feed supply chamber communicating with said passage and thepressure in the passage being applied to the surface of the liquid insaid supply chamber, meansfor delivering feed liquid to the supplychamber, a compressor outlet line communicating with the reactionchamber, the compressed vapors being discharged at high velocity throughthe outlet line, a feed line extending from beneath the liquid level insaid supply chamber and opening into said compressor outlet line, thefeed liquid being drawn into the last mentioned line by the highvelocity vapors.

8. A distillation system embodying a reaction chamber, a heatercommunicating with said chamber and adapted to receive and superheatvapors from the chamber, a separating chamber into which the vapors fromsaid heater are discharged, a compressor communicating with saidseparating chamber and adapted to compress a portion of the superheatedvapors discharged into the separating chamber, a liquid feed supplychamber, the'pressure of the superheated vapors from the heater, beingapplied to the surface of the liquid in said supply chamber, means fordelivering feed liquid to the supply chamber, a compressor outlet linecommunicating with the reaction chamber, the compressed vapors beingdischarged at high velocity through the outlet line, and a feed lineextending from beneath the liquid level in said supply chamber andopening into said compressor outlet line, the feed liquid being drawninto the last mentioned line by the high velocity vapors.

9. A petroleum distillation system embodying a reaction chamber, asuperheater communicating with said chamber and adapted to receive andcrack all of the vapors from the chamber, a compressor communicatingwith said heater and adapted to compress one portion only of the vaporsdischarged from the heater, means for mixing the compressed vapors aftercompression with feed liquid and for delivering the mixture to saidreaction chamber, means for removing unvaporized residual liquid fromthe chamber, means communicating with said heater and adapted toseparate another portion of the superheated vapors discharged from theheater into liquid and gaseous fractions.

10. A petroleum distillation system embodying a reaction chamber, aheater communicating with said chamber and adapted to receive and crackall of the vapors from the chamber, acompressor communicating with saidheater and adapted to compress one portion only of the vapors dischargedfrom the heater, means for mixing the compressed vapors aftercompression with feed liquid and for delivering the mixture to saidreaction chamber, means for removing unvaporized residual liquid fromthe chamber, apparatus communicating with said heater and adapted toseparate another portion of the superheated vapors discharged from theheater into liquid and gaseous fractions, and means for regulating thepressure in said apparatus, thereby controlling the pressure of thesuperheated vapors in the system.

ANDREW L. STILL.

